Aluminum coating process and flux



/t f G L Patented Mar. 9, 1954 2,671,737 ALUMINUM COATING PROCESS ANDFLUX Walter E. Jominy, Detroit, and John H. Olson,

Berkley, Mich., assignors to Chrysler Corporation, Highland Park,

Delaware Mich., a corporation of I No Drawing. Application October 10,1950,

. Serial No. 189,478

8 Claims. (Cl. 11'751) This invention relates to improvements in theformation of aluminum and aluminum alloy coatings on steel and moreparticularly to an improved process and flux for forming an integraltype bond between aluminum or aluminum alloy and steel.

One of the main objects of the invention is to provide a flux of thiskind which may be applied to the steel to be aluminum coated in the formof a fluent aqueous mixture or suspension of salts, a paste of salts, ora fused mass of salts.

Another object of the invention is to provide a flux of this kind whichadheres tenaciously to the steel and which is not completely melted,burned on or otherwise injured or removed during dipping in a moltenaluminum bath until it has been submerged in the molten aluminum.

A further object of the invention is to provide a flux of this kindwhich readily melts and disappears when an article coated with it issubmerged in molten aluminum, in order to expose unoxidized surfaceportions of the article to the molten aluminum.

An additional object of the invention is to provide a flux of this kindwhich 'provides a substantially integral bond between aluminum andferrous metal as well as other metals during immersion of such metals inmolten aluminum.

In practicing the improved aluminum or aluminum alloy coating proces,the metal to be coated, preferably ferrous metal or metal of the irongroup, is first coated with an oxide reducing and air excluding coatingof flux which tenaciously adheres to the metal to be treated and whichdoes not melt or break down until the flux coated metal is immersed in amolten aluminum or aluminum alloy bath. The flux coating formed andapplied according to our invention remains intact on the metal to betreated as the metal is projected, in accordance with conventionalpractice, into the molten aluminum or aluminum alloy bath and that partof the metal being coated immediately adjacent the surface of the bathand yet exposed to the atmosphere above the bath remains coated withflux during immersion of successive adjacent portions of the metal beingtreated as the latter is slowly projected into the bath.

Our improved flux may comprise a fluent aqueous mixture or suspension ofcertain hereinafter recited salts or it may be produced as a paste ofcertain salts hereinafter set forth in which a small amount of water isincluded as a binder. If desired, the flux may be employed in the formof a fused mass of certain salts hereinafter set forth into which themetal to be aluminum coated may be dipped in order to deposit thereon alayer of fused salts which immediately solidify at room temperature.

The suspension form of the flux may be produced by mixing in parts ofwater by weight the following proportions of salts:

Parts by weight The following proportions within the above range arepreferred:

Parts by weight Sodium fluosilicate (NaaSiFs) 4to 20 Potassium chloride(KCl) 3 to 5 Sodium chloride (NaCl) 3 to 5 Sodium fluoride (NaF) orcryolite (NasAlFs) 0.8 to 5 In the foregoing formulas, either sodiumfluoride or cryolite, a common name for sodium aluminum fluoride, may beemployed. The above portions of salts produce a suspension into whichthe ferrous or other metal parts to be aluminum coated are dippedfollowing cleaning of them and while the flux suspension is heated toslightly under a boiling temperature. When parts are removed from thesuspension, they carry with them a continuous film of the suspensionwhich rapidly 'dries because of the temperature to which the suspensionis heated and under the influence of the heat imparted from thesuspension to the work. As the suspension dries, a substantially airimpervious crust-like film of the salts of the suspension is formed onthe work in a way which produces an oxide reducing and air excludingenvelope about the work.

After the flux coating has dried. the work may be inserted in a moltenbath of aluminum or aluminum alloy. The aluminum and aluminum alloy bathneed not be chemically pure. The immersion of the flux coated workpreferably takes place while the bath is at a temperature slightly aboveits melting point.

The paste type flux may be formed by mixing together substantially 15parts by weight of zinc chloride, 35 parts by weight of sodium chloride,25 parts by weight of potassium chloride and 25 parts by weight ofcryolite. Sufficient water is added to this mixture to bring the pasteto a desired consistency such that it may be con- 3 veniently b hed orotherwise applied on to the work. 'I'h; layer of flux paste is allowedto dry thoroughly before the flux paste coated work is immersed inmolten aluminum in accordance with the above procedure.

The fused salt type flux preferably comprises substantially equal partsof zinc chloride, sodium chloride, potassium chloride and either sodiumfluoride or cryolite, the chemical composition of which is set forthabove. This mixture of salts is preferably heated to and maintained atapproximately 1200 F. The work to be aluminum coated is dipped into thefused salt bath and removed and retained at atmospheric tempera-' turessufliciently long for the coating of fused salts to solidify. The thuscoated work is then immersed in a molten aluminum or aluminum alloy bathin accordance with the above specified procedure.

It is found that work aluminum coated in accordance with the aboveprocess, by immersing it in an aluminum or aluminum alloy bath while thesurfaces of the work are covered with flux coatings of any of theforegoing types, is characterized by substantially integral bondsbetween the metal work and the aluminum layer. All of the ingredients ofthe various formulas of the flux are comparatively inexpensive andreadily available.

Although but several specific embodiments of our invention have beendescribed, it is understood that various changes in the materialsemployed and in the sequence of steps as well as in the temperature andperiods of heating may be made without departing from the spirit of ourinvention.

We claim:

1. A fluent aqueous flux for conditioning ferrous metal for thereception of an adherent immersion formed coating of aluminum, said fluxconsisting of the following substances as essential constituents and insubstantially the proportions given: 100 parts by weight of water, 2 to40 parts by weight of sodium fluosilicate, 2 to parts by weight ofsodium chloride, 2 to 10 parts by weight of potassium chloride and 0.2to 40 parts by weight of sodium fluoride.

2. A fluent aqueous flux for conditioning ferrous metal for thereception of an adherent immersion formed coating of aluminum, said fluxconsisting of the following substances as essential constituents and insubstantially the proportions given: 100 parts by weight of water, 2 to40 parts by weight of sodium fluosilicate, 2 to 10 parts by weight ofsodium chloride, 2 to 10 parts by weight of potassium chloride and 0.2to 40 parts by weight of sodium aluminum fluoride.

-3. The process of forming corrosion resisting coatings consistingessentially of aluminum on ferrous metal bodies which consists incoating the ferrous metal with an adherent fluent aqueous fluxconsisting of the following substances as essential constituents and insubstantially the proportions given: 100 parts by weight of water, 2 to40 parts by weight of sodium fluosilicate, 2 to 10 parts by weight ofsodium chloride, 2 to 10 parts by weight of potassium chloride, and 0.2to 40 parts by weight of a compound selected from the group consistingof sodium fluoride and sodium aluminum fluoride; forming a continuouscoating of said flux on said metal which upon drying will provide anoxide reducing and air excluding film of the salts of the flux thereon,drying said coating and immersing said flux coated metal in a moltenmetal bath consisting essentially of aluminum.

4. A fluent aqueous flux for conditioning ferrous metal for thereception of an adherent immersion formed coating of aluminum, said fluxconsisting o1 the following substances as essential constituents and insubstantially the proportions given: 100 parts by weight of water, 2 to40 parts by weight of sodium fluosilicate, 2 to 10 parts by weight ofsodium chloride, 2 to 10 parts by weight of potassium chloride, and 0.2to 40 parts by weight of a compound selected from the group consistingof sodium fluoride and sodium aluminum fluoride.

5. A fluent aqueous flux for conditioning ferrous metal for thereception of an adherent immersion formed coating 01' aluminum, saidflux consisting of the following substances as essential constituentsand in substantially the proportions given: 100 parts by weight ofwater, 4 to 20'parts by weight of sodium fluosilicate, 3 to 5 parts byweight of sodium chloride, 3 to 5 parts by weight of potassium chloride,and 0.8 to 5 parts by weight of a compound selected from the groupconsisting of sodium fluoride and sodium aluminum fluoride.

6. The process of forming corrosion resisting coatings consistingessentially of aluminum on ferrous metal bodies which consists incoating the ferrous metal with an adherent fluent aqueous fluxconsisting of the following substances as essential constituents and insubstantially the um aluminum fluoride; forming a continuous 1 coatingof said flux on said metal which upon drying will provide an oxidereducing and air excluding film of the salts of the flux thereon, dryingsaid coating and immersing said flux coated metal in a molten metal bath'consisting essentially of aluminum.

WALTER E. JOMINY. JOHN H. OLSON.

References Cited in the flle of this patent UNITED STATES PATENTS OTHERREFERENCES Handbook of Chemistry & Physics, 27th 136. (1943) pages 456,457, 458, 459, published by Chemical Rubber Publishing 00., Cleveland,Ohio.

3. THE PROCESS OF FOMRING CORROSION RESISTING COATINGS CONSISTINGESSENTIALLY OF ALUMINUM ON FERROUS METAL BODIES WHICH CONSISTS INCOATING THE FERROUS METAL WITH AN ADHERENT FLUENT AQUEOUS FLUXCONSISTING OF THE FOLLOWING SUBSTANCES AS ESSENTIAL CONSTITUENTS AND INSUBSTANTIALLY THE PROPORTIONS GIVEN: 100 PARTS BY WEIGHT OF WATER, 2 TO40 PARTS BY WEIGHT OF SODIUM FLUOSILICATE, 2 TO 10 PARTS BY WEIGHT OFSODIUM CHLORIDE, 2 TO 10 PARTS BY WEIGHT OF POTASSIUM CHLRIDE, AND 0.2TO 40 PARTS BY WEIGHT OF A COMPOUND SELECTED FROM THE GROUP CONSISTINGOF SODIUM FLUORIDE AND SODIUM ALUMINUM FLUORIDE; FORMING A CONTINUOUSCOATING OF SAID FLUX ON SAID METAL WHICH UPON DRYING WILL PROVIDE ANOXIDE REDUCING AND AIR EXCLUDING FILM OF THE SALTS OF THE FLUX THEREON,DRYING SAID COATING AND IMMERSING SAID FLUX COATED METAL IN A MOLTENMETAL BATH CONSISTING ESSENTIALLY OF ALUMINUM.